Device for liquid treatment of wafer-shaped articles

ABSTRACT

A device for liquid treatment of a defined area of a wafer-shaped article, especially of a wafer, in which a mask is kept at a defined short distance to the wafer-shaped article such that liquid can be retained between the mask and the defined area of the wafer-shaped article by capillary force.

BACKGROUND OF THE INVENTION

The invention relates to a device and a process for liquid treatment ofa defined area of the main surface of a wafer-shaped article, especiallya wafer.

The reason for treatment of a defined section of a wafer-shaped article,i.e. the section near the edge, especially of a wafer, will be describedbelow.

A wafer, for example a silicon wafer, can have for example a coating ofsilicon dioxide on all sides. For subsequent processes (when for examplea gold layer or a layer of polysilicon (polycrystalline silicon) is tobe applied) it can be necessary to remove the existing coating from thewafer at least in the edge area of the main surface, but also optionallyin the area of its peripheral surface and/or the second main surface.This takes place by etching processes which can be divided mainly intodry etching processes and wet etching processes. It can also bedesirable to remove a metal (for example, copper) which was appliedgalvanically beforehand from certain areas of the main surface of thesemiconductor substrate. In this case, this area can be either anannular section near the edge, or exactly the area of the front mainsurface (main surface on which the structures are located=device side),in which there are no structures, i.e. the chip-free zone.

Another application is the cleaning of wafers. Here it can be necessaryto clean the wafer at least in the edge area of the main surface, butoptionally also in the area of its peripheral surface and/or the secondmain surface, i.e. to remove particles and/or other contamination. Thisis done by wet cleaning processes.

Another liquid treatment is the application of layers, for examplegalvanic application of metals (electroplating). This can be done withor without current, in the latter case its being “ElectrolessElectroplating”.

The invention is aimed at wet etching, wet cleaning or wet chemicalapplication of layers (combined under the concept of liquid treatment).The surface section of the wafer to be treated is wetted with thetreatment liquid and the layer to be removed or the impurities areremoved or a layer is built up in this surface section.

During liquid treatment the wafer-shaped article can be eitherstationary or can rotate (for example, around an axis).

To prevent the treatment liquid from reaching the surface not to betreated in an uncontrolled manner, EP 0 316 296 B1 suggests a carrier(chuck) which flushes the surface, which faces the carrier and which isnot to be treated, with a gas. In doing so the gas emerges between theedge of the wafer and the carrier.

JP 09-181026 A describes a carrier for semiconductor wafers whichoutside an annular nozzle has a special shape, for example an annularstep which falls off to the outside, or a bevel of its edge. An intakeopening is also proposed. The flow velocity in the edge area will beinfluenced (reduced) by this shaping or by the intake opening. This isintended to be used to allow the treatment liquid applied from the topto flow beyond the edge of the wafer onto the side facing the chuck andto treat an edge area there.

Regardless of whether a means for accommodating the wafer-shaped article(carrier or chuck) as claimed in EP 0 316 296 B1 or JP 09-181026 A(English abstract) is used, on the main surface facing the carrier anedge area of 1.5 mm (measured from the outer edge of the wafer) atmaximum is treated. Afterwards, the liquid flows back in the directionof the wafer edge and is flung off by it. This treated edge area is notintentionally defined in either of the two cases, rather it is a randomresult, since the size of the edge area depends largely on a pluralityof parameters which mutually influence one another to some extent, suchas the surface composition (roughness, type and thickness of theadsorption layers), temperature, pressure, humidity, etc.

U.S. Pat. No. 4,838,289 A discloses a system for etching the edge of awafer, in which a nozzle is pointed against the area of the wafersurface to be treated while the wafer rotates. The defect of this systemis that the area to be treated is not exactly defined and also liquidcan reach the area which is not to be treated.

SUMMARY OF THE INVENTION

Accordingly, the object of the invention is to enable treatment of adefined section with a liquid on the surface of a wafer-shaped article,and it will also be possible among others to treat an edge area of morethan 2 mm (measured from the outer edge of the wafer-shaped article).This defined section can also be an inner area of the surface of thewafer-shaped article, i.e. the area which does not extend to the edge ofthe wafer-shaped article. If here too one area at a time is bordered bya circular line to the outside and/or inside, this is still unnecessary;the area to be treated can also be bordered for example by a polygon.This boundary line can, if the wafer-shaped article is a wafer,correspond to the area of the surface on which the chips are located(“device area”). Accordingly either the inner chip area or the outerchip-free area can be treated.

Accordingly, in its most general embodiment the invention proposes adevice for liquid treatment of a defined section of the wafer-shapedarticle, especially a wafer, consisting of holding means for holding thewafer-shaped article, a mask which in shape and size corresponds to thearea of the defined section which is to be treated with liquid, andspacer means which keep the mask and the wafer-shaped article at adefined small distance to one another such that liquid can be retainedbetween the mask and the defined area of the wafer-shaped article bycapillary forces.

Holding means can be among others vacuum grippers, gripping means whichtouch the wafer-shaped article on its peripheral-side edge, or aso-called Bernoulli chuck.

The mask is made such that, when a wafer-shaped article (wafer) islocated on the carrier, the mask does not touch the wafer-shaped article(wafer), i.e. a gap remains between the wafer and the mask. The maskprojected perpendicularly onto the main surface of the wafer indicatesthe area of the wafer which is treated with liquid. The material of thesurface of the mask which is facing the wafer-shaped article should bechosen such that it is wetted by the liquid so well that liquid is keptin the gap between the wafer-shaped article and the mask by capillaryforce. The sum of the two wetting angles of the liquid on the one handagainst the wafer-shaped article and on the other hand against the maskshould be less than 180°, preferably less than 150°. In the preselectedmask surface this can of course be achieved also by additives which areadded to the liquid (wetting agents).

One advantage of the device as claimed in the invention is that thearticle to be treated is wetted exactly in the area to be treated by thetreatment liquid, without this area being touched by a solid. At thesame time the liquid droplets are prevented from reaching areas whichare not to be treated or should not be treated.

In one advantageous embodiment the mask has the shape of a ring. In thiscase the ring can have an inside diameter which is less than the outsidediameter of the wafer-shaped article, and an outside diameter which isat least the same size as the outside diameter of the wafer-shapedarticle. This can be necessary when the surface to be treated likewisehas the shape of a ring, as is the case for example when removing alayer from a defined edge area of a semiconductor wafer.

It is advantageous if the spacer means keep the mask and thewafer-shaped article at a distance of 0.05 to 1 mm to one another. Whenusing thin liquid media such as water, solvents or various acids in anaqueous solution, the liquid is easily prevented from running out of thecapillary area between the mask and the wafer-shaped article.

In one embodiment the spacer means consists of gripper elements whichare in direct contact with the wafer-shaped article and are joineddirectly or indirectly to the mask. This can take place for example byan outside rod (indirectly) or by for example pins located on theperipheral side (directly).

In another embodiment the mask and holding means are stationary relativeto one another with respect to rotation around an axis which isperpendicular to the mask. The mask and the holding means therefore bothdo not rotate or, for example the holding means rotates, and with it thewafer-shaped article, thus the mask rotates at the same time with thesame speed. The lack of relative motion of the mask to the surface ofthe wafer-shaped article is advantageous when the liquid held in thecapillary area between the mask and the wafer-shaped article, while itis kept in this area, should experience as little motion in itself aspossible. This prevents reaching into the area which is not to betreated by the liquid.

The spacer means can consist of a gas feed means which is joineddirectly or indirectly to the mask and is pointed against thewafer-shaped article, by which the wafer-shaped article can be kept on agas cushion. This gas feed means can be for example one or more nozzleslocated perpendicular or slantwise to the surface of the wafer-shapedarticle or an annular nozzle. By choosing the pressure and the gasvolume flow, for a stipulated shape, size and arrangement of the gasfeed means the distance between the gas feed means and the wafer-shapedarticle and thus the distance between the mask and wafer-shaped articlecan be adjusted exactly and reproducibly.

Furthermore, the device of the invention can have in one embodimentdistance changing means which can increase the distance between the maskand the wafer-shaped article to one another such that liquid which islocated between the mask and wafer-shaped article is no longer held bycapillary forces. Here it can be a movement mechanism which can move theholding means perpendicular to the surface of the wafer-shaped articleor a movement mechanism which can move the mask accordingly. But thewafer-shaped article can also be directly moved accordingly. A distancechanging means can be for example an additional gripper (for example,spoon) or there are pins (lifting pins) which lift the wafer-shapedarticle. The distance changing means can also be a gas feed means withan operating state which can be changed such that the wafer-shapedarticle is raised or lowered.

The mask and the wafer-shaped article are moved apart from one anotherby one such distance spacing means such that the liquid which is foundin the area in between can be removed again. It is advantageous if thedistance changing means can increase the distance by at least 0.2 mm,preferably at least 0.5 mm.

It is advantageous if the distance changing means are made such thatthey can change the distance between the mask and the wafer-shapedarticle during or immediately after liquid treatment. This is possiblefor example in the case of the gas feed means as a distance changingmeans.

In one embodiment, the distance changing means and spacer means are madesuch that elements of the spacer means are at the same time elements ofthe distance changing means. If the spacer means has pins with thecorresponding notches which touch the wafer-shaped article on theperipheral side and thus keep it at a defined distance to the mask,these pins are at the same time an element of the distance changingmeans when they can be moved perpendicularly to the surface of thewafer-shaped article.

In one embodiment, essentially perpendicular to the main surface of thewafer-shaped article, there are guide elements which border the positionof the wafer-shaped article on the peripheral side. In this way theposition of the wafer-shaped article is fixed against the mask withrespect to displacement. The distance of the guide elements to thecenter of a wafer-shaped article can be variable.

This distance can also be reduced to such a small amount that the guideelements can secure the wafer-shaped article and they are in thisrespect also an element of the holding means. The holding means can alsoconsist of guide elements and also a gas feed means.

A device in which the distance changing means consists of a gas feedmeans which is connected directly or indirectly to the mask and ispointed against the main surface of the article, by which thewafer-shaped article can be held on a gas cushion [sic]. Here the gasfeed means need not necessarily be spacer means at the same time, sincethe spacer means can be a simple mechanical support (for example, pins,spacer ring) and the gas feed means routes gas only when thewafer-shaped article is lifted.

But the spacer means and the distance changing means can also beessentially the same gas feed means, means being provided by which thegas feed means can be shifted into at least two different operatingstates. By means of these at least two different operating states, atleast two different distances between the wafer-shaped article and themask can be set. These means are for example means which can change thepressure and/or the volumetric flow of the gas supplied to the gas feedmeans. These means are for example reducing valves or valves which openand close the additional nozzles of the gas feed means. At a highervolumetric flow the wafer-shaped article then assumes a greater distanceto the mask than at a lower volumetric flow. Other means can change thesize, shape and/or the alignment of the gas feed means. If for examplemovable nozzles are used, the wafer-shaped article is lifted the moredramatically, the larger the angle (0° to 90°) is chosen to be betweenthe nozzle alignment and surface of the wafer-shaped article againstwhich the nozzle is pointed.

Spacer means and distance changing means can also be two gas feed meanswhich can be triggered separately from one another.

In one embodiment the holding means can be caused to rotate, by whichthe wafer-shaped article rotates. This is, even if not necessary,advantageous since the treatment liquid can be flung off both from thecarrier and also from the wafer edge.

This gap between the mask and the wafer-shaped article in the embodimentis 0.05 to 1 mm, advantageously 0.1 to 0.5 mm. Thus, between the waferand the gas guide device a type of capillary forms by which the liquidwhich has flowed around the wafer edge is sucked. The inside diameter ofthe surface which faces the gas guide device and which is wetted by theliquid is less than the inside diameter of the annular surface of thegas guide device.

It is advantageous when the surface of the gas guide device facing thewafer-shaped article is parallel to the main surfaces of thewafer-shaped article. The gap between the wafer-shaped article (wafer)and the gas guide device is thus the same size in the entire edge area.

One embodiment calls for the carrier to be able to be rotated. This is,even if not necessary, advantageous since the treatment liquid can beflung off both from the carrier and also from the wafer edge. If thecarrier is not in rotation during liquid treatment, the liquid can beblown off by a gas stream (from a gas feed means).

In addition, the device can have a liquid line which is pointed at thesurface of the wafer-shaped article facing the mask. In this way thesurface with a defined first area which has not been treated with afirst liquid can also be treated with a second liquid and in the secondarea it is different from the first. This second area can be largersuperficially and also completely cover the first area. If the firstliquid is for example an etching liquid, it can be removed withoutresidue from the surface facing the mask using the second liquid (forexample, deionized water). At the same time the mask can also be cleanedor liquid can be removed from it.

BRIEF DESCRIPTION OF THE INVENTION

Other details, features, and advantages of the invention result from thefollowing description of the embodiments of the invention shown in thedrawings.

FIGS. 1-5 schematically show axial sections 5 of different embodimentsas claimed in the invention.

FIGS. 6-8 show a schematic axial section of an embodiment as shown inFIG. 1 in different operating states.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows one embodiment of the device 1 of the invention. The device1 consists of an essentially round base body 4 to which the mask 2 whichhere has the shape of a ring is concentrically attached. But the ring 2can also be machined out of the base body. The ring 2 has an outsidediameter which is larger and an inside diameter which is smaller thanthe outside diameter of the wafer. Pins 3 which are mounted on the ring2 hold the wafer W on the peripheral side. The pins 3 have a notch 31which locks into the wafer edge and thus keep the wafer in a definedhorizontal position. The pins 3 with their notches 31 represent thespacer means to the mask 2. Between the mask 2 and the wafer surface Wfa defined gap 15 is thus established. The pins 3 are moved via amechanism which is not shown relative to an axis A in order to grip thewafer securely and to remove or to lift the wafer to release it again.Within the base body 4 there is a lifting mechanism 5 (distance changingmeans) which can be moved up and down in the direction L of the arrow,and can change the distance between the wafer W and the mask 2. Thelifting mechanism consists of a carrier which has an essentially planesurface which is parallel to the wafer, which faces the wafer and which,when the carrier is lifted, touches the wafer only on its lower surfaceWf and then lifts the wafer. The entire device 1 and with it the wafercan rotate around the wafer axis A.

The treatment liquid can be applied either by the nozzle 7 which ismounted outside in the vicinity of the wafer edge or by a nozzle 6 whichis pointed against the wafer surface Wb facing away from the mask 2. Inthe first case (nozzle 7) an amount 20 of liquid is applied directly tothe mask 2 near the wafer edge. The liquid is then pulled in by thecapillary-like gap 15 and thus precisely wets the area of the wafersurface Wf which is assigned to the mask 2 and which is overlapped byit. In the second case (nozzle 6) an amount 18 of liquid is applied tothe surface Wf facing away from the mask 2, for example in its center,the liquid runs then radially to the outside to the wafer edge; this canbe supported by rotation of the wafer. Thereupon the liquid flows aroundthe wafer edge and is pulled in by the gap 15. In both cases the wafercan rotate during the entire liquid treatment (R); this has theadvantage that excess liquid which does not penetrate into the gap 15cannot flow down uncontrolled over the mask 2, but is flung off in acontrolled manner. Then a second liquid (for example, deionized water)is applied to the wafer surface Wf facing the mask 2 via the liquid line28, at the same time the carrier 4 rotates, by which the second liquiddisplaces the liquid which is located in the gap 15. At the same time,before or even afterwards the wafer is lifted with the lifting mechanism5.

FIG. 2 shows another embodiment. The mask 2 (ring) is supported by thedisk 8. The wafer W is held by a rotating vacuum chuck 13 on its surfaceWb facing away from the mask. This has the advantage that neither thewafer edge nor the wafer surface Wf facing the mask are touched. Boththe chuck 13 holding the wafer W and also the mask 2 can be turnedaround the same axis A, the chuck in direction Rw and the mask indirection Rm. If this takes place with the same rotational speed and inthe same direction, the mask and the wafer are not moved relative to oneanother (Rw=Rm). The chuck 13 and the mask 2 are connected to oneanother via the distance changing means 5 and are moved by it away fromand towards one another (arrow L). This distance changing means 5 can befor example a pneumatic cylinder or a spindle. Using this distancechanging means 5 the gap 15 between the wafer and mask can be setexactly, therefore it represents a spacer means at the same time. Thenozzle 7 applies an amount 20 of liquid directly to the mask 2 near thewafer edge. The liquid is then pulled in by the capillary-like gap 15.

FIG. 3 shows a third embodiment. The device 1 consists of a bath tank 27in which there is a pot-shaped carrier 14. The space 23 within thecarrier is sealed against the bath 26 which is located between thecarrier and bath tank. The carrier 14 can be lifted from the bath 26using the lifting mechanism. The upper edge of the carrier has the shapeof a ring 2 which represents the mask, with a surface which faces thewafer W and which is plane-parallel to its surfaces Wf. On this ring 2(mask) there are pins 3 with notches which keep the wafer at a defineddistance to the mask, by which a gap 15 forms. The carrier 14 with thewafer W located on it is lowered into the bath (L1) so far that theliquid level is located somewhat above the ring so that the wafer edgeis wetted. The liquid is pulled by capillary forces into the gap 15between the wafer and mask. To prevent the penetration of liquid intothe space 23 within the carrier as a result of the negative pressure init, the space is connected via the tube 25 to the environment. A slightoverpressure can also be built up via this tube 25 in the space 23within the carrier, and the carrier is again lifted out of the bath(L1). After liquid treatment, the liquid located in the gap 15 is forcedradially to the outside using the stronger overpressure which has beenbuilt up by a gas which has been supplied through the tube 25. The gap15 can also be enlarged with the distance changing means 5. Here fourpins 5 which can move up and down are shown; they can touch the waferwithin the mask 2 on its surface assigned to the mask and can lift itvertically (L2).

FIG. 4 shows a fourth embodiment. The device consists of a bath 14 inwhich the treatment liquid is located and which can be moved up and down(arrow L1), and of a carrier 11. The carrier 11 consists of a base body4 and a ring 2 which is molded on underneath. Pins 3 with notches whichare made underneath on the ring 2 hold the wafer W on the peripheralside, at a defined gap distance to the ring 2 so that the wafer in thehorizontal position is suspended underneath on the carrier. The carrier11 together with the wafer W is immersed into the bath tank 27 so farthat the liquid level wets the ring 2 and thus the surface Wb of thewafer facing away from the ring and the peripheral-side wafer edge arecompletely wetted. The liquid penetrates into the gap between the waferand ring. The carrier 11 is lifted out of the bath after treatment. Avacuum-pickup 5 which is mounted within the carrier is moved down sothat it touches and suctions the wafer on the surface Wf of the waferfacing the mask. Afterwards the wafer is moved farther down with thepickup and thus the capillary force, by which the liquid is held withinthe gap 15, is overcome. By rotating the pickup the liquid residueremaining on the wafer may be flung off.

FIG. 5 shows one embodiment. The device consists of a carrier 11 which[has] a base body 4, and of a ring 2 which is attached via spacers 41 ata distance to the base body on the latter. The ring is over the spacerparts 41. On the ring 2 pins 53 are attached which, referenced to theaxis of rotation A of the carrier 11, can be moved radially to theoutside and can surround the wafer W on the peripheral side. The pins 53have the shape of a small cylinder with their axes perpendicular to thesurface of the wafer. Gas channels 44 and 45 are machined into the basebody 4 and they discharge into gas nozzles 46 and 49 against which thesurface of the wafer facing the carrier 11 is pointed. The nozzles 46and 49 are positioned obliquely to the outside, the nozzles 49 lyingfarther to the inside being positioned less obliquely than the nozzles46 which lie farther to the outside, i.e. the emerging gas flow G1 ofthe nozzles 46 which lie farther to the outside strikes the wafersurface at a flatter angle than the emerging gas flow G2 of the nozzleswhich lie farther to the inside. The distance of the base body 4 to thewafer W in the area 48 between the inner and outer nozzles 49 and 46 issmaller than in the area 47 outside the outer nozzles 46. Both thenozzles 49 which lie to the inside and also the nozzles 46 which lie tothe outside can be selectively either a plurality of nozzles arranged ina circle, or can have the shape of annular nozzles.

This device can be operated in essentially two different ways. In thefirst operating mode the outer gas flow G1 and the inner gas flow G2 canbe turned on and off separately from one another. If only the first gasflow G1 is turned on, the gas flows only over the area 47. The wafer Wis only slightly lifted, by which a small capillary-like gap 15 formsbetween the mask 2 and the wafer W. If in this first operating state aliquid, as is described in the description to FIG. 1, is applied, it ispulled into the gap 15. If at this point, in addition or instead of thegas flow G1, the gas flow G2 is turned on, gas flows not only over thearea 47 outside of the outer nozzles 46, but also over the area 48between the outer and inner nozzles. By means of this second operatingstate the wafer W is lifted somewhat, shown by the dotted line. Thewafer edge slides along the cylinder surface of the pins 53. This slightlifting of the wafer is enough for the liquid in the gap 15 between themask and wafer to no longer be held by the capillary forces. The liquidcan be removed from this area; this takes place by the gas flow, i.e.the droplets are blown away radially to the outside. Removal of theliquid can be supported by the entire carrier 11 and with it the waferrotating. In addition, by means of a nozzle which is supplied by theliquid line 28, flushing liquid can be routed through the base body 4 tothe wafer surface facing the carrier, by which the liquid in the gap 15is additionally displaced. This flushing liquid must for its part ofcourse also be removed again.

In the second operating mode the two gas flows G1 and G2 are jointlyconnected. In the first operating state less gas flows than in thesecond operating state, by which the wafer in the second operating stateassumes a position in which its distance to the mask 2 is larger than inthe first operating state. The distance of the wafer W to the mask 2 inthe first operating state is for example 0.5 mm and in the second 0.8mm.

Using FIGS. 5-8 the operating mode of a device as claimed in theinvention will be described, proceeding from the embodiment of FIG. 1.First of all, the wafer W is moved into the vicinity of the mask 2, bywhich the gap 15 forms. The defined distance between the mask 2 and thewafer is ensured by spacer means, here the pins 3 (FIG. 6) with notches.At this point liquid is applied either to the wafer surface Wb facingaway from the mask or directly to the wafer edge. The liquid in partenters the gap 15 (F2). The excess part of the liquid F1 runs down andis thrown off when the mask and/or the wafer rotate. The liquid cannotrun farther to the inside than the inner contour of the mask 2, i.e. itpenetrates only to the point P. The distance a1 between the mask 2 andthe wafer is chosen to be so small that the liquid is held by capillaryforces within the gap 15, and treats the wafer surface there. A liftingmechanism 5 now comes into contact with the wafer surface Wf which facesthe mask 2, the pins 3 are now opened (B) and the lifting mechanism 5lifts the wafer such that the liquid film in the gap 15 tears and onlymore drops 16 remain on the mask and/or on the wafer surface. Thesedrops 16 can now be rinsed off, blown off and/or flung off.

1. Device for liquid treatment of a defined section of a wafer-shapedarticle (W), especially of a wafer, comprising: holding means forholding the wafer-shaped article; a mask which in shape and sizecorresponds to the area of the defined section which is to be treatedwith liquid, wherein the mask and holding means are stationary relativeto one another with respect to rotation around an axis (A) which isperpendicular to the mask; spacer means which keep the mask and thewafer-shaped article at a defined short distance to one another suchthat liquid can be retained between the mask and the defined area of thewafer-shaped article by capillary forces; and a liquid line which ispointed at the surface of the wafer-shaped article facing the mask,wherein the elements of the spacer means are at the same time elementsof a distance changing means which can increase a distance between themask and the wafer-shaped article such that the retained liquid is notlonger held by capillary forces.
 2. Device as claimed in claim 1,wherein the mask (2) has the shape of a ring.
 3. Device as claimed inclaim 2, wherein the ring has an inside diameter which is less than theoutside diameter of the wafer-shaped article, and an outside diameterwhich is at least the same size as the outside diameter of thewafer-shaped article.
 4. Device as claimed in claim 1, wherein thespacer means keep the mask and the wafer-shaped article at a distance(a1) of 0.05 to 1 mm.
 5. Device as claimed in claim 1, wherein thespacer means consists of gripper elements (3, 53) which are in directcontact with the wafer-shaped article and are joined directly orindirectly to the mask (2).
 6. Device as claimed in claim 1, wherein thespacer means comprises a gas feed means (45, 46) which is joineddirectly or indirectly (41) to the mask (2) and is pointed against thewafer-shaped article, by which the wafer-shaped article can be kept on agas cushion.
 7. Device as claimed in claim 1, with guide elements (3,53) which border the position of the wafer-shaped article on theperipheral side and which are located essentially perpendicular to themain surface of the wafer-shaped article.
 8. Device as claimed in claim7, wherein the holding means comprises of guide elements (53) and a gasfeed means (45, 46).
 9. Device as claimed in claim 1, wherein thedistance changing means comprises a gas feed means (44, 49) which isjoined directly or indirectly to the mask (2) and is pointed against themain surface (Wf) of the wafer-shaped article, by which the wafer-shapedarticle can be kept on a gas cushion.
 10. Device as claimed in claim 1,wherein the spacer means and the distance changing means are essentiallythe same gas feed means (44, 45, 46, 49), and there are means by whichthe gas feed means can be shifted into at least two different operatingstates, by which two different distances between the wafer-shapedarticle and the mask can be adjusted.